The electronic properties of GaN doped with three transition metal impurities (titanium, nickel and gold) have been calculated using a density functional approach. Both substitutional and interstitial mechanisms for dopant incorporation have been considered, together with the effect of varying the charge state of the impurity. The electrical activity of the metal impurities is characterized by considering the defect levels in the band gap, the Mulliken charges on the atoms and the local distribution of valence charge density. The calculated formation energies indicate that a substitutional mechanism is preferred and that all three metals act as donor dopants.
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